The process of forming Cu plating on a substrate by electrolytic plating broadly includes two steps. First, a metal thin film (seed layer) used for feeding power is formed in advance on a substrate (wafer) surface on which plating needs to be formed. Then, the substrate having the seed layer formed thereon is fixed to a jig for power feeding, and immersed in a plating solution. Then, power is fed to the seed layer, thereby forming plating (for example, PTD 1).
In PTD 1, oxygen plasma is applied to a resist opening in the seed layer formed on the substrate before plating (paragraphs [0008] to [0010]). This is for the purpose of forming a thin oxide film on the surface of the seed layer by applying oxygen plasma, to improve the wettability of the seed layer to the plating solution.